Tanning with esters of chloroformic acid in an nonaqueous medium



Patented Sept. 26, 1950 UNITED STATES PATENTVOFF'ICEQ TANNING WITH ESTERS oF oHLoRo FORMIC ACID IN A NONAQUEOUS MEDIUM Robert C. Putnam, Marblehead, Mass, assignor to United Shoe Machinery Corporation, Flemington, N. J a corporation of New Jersey No Drawing. Application April 23, 1947, Serial My invention relates to the treatment of hidesotherwise pretreated skins or hides are subj eoted to various steps including a prolonged soaking treatment in a solution containing various vegetable extracts. occupies a period of several weeks and involves extensive handling of the hides.

By either of these common methods of tanning, extended periods of time are required sq that to insure continuous production of leather a very large number of skins or hides must be maintained in various stages of tanning. Investment in skins or hides and in treating tanks, vats,

or other treating equipment is large so that the cost of the ultimate leather is high.

It is an important feature of my invention to convert skin and hide material to a stable nonputrescible leather-like condition by a short and simple treatment of the skin or hide materials with a new type of reagent. By my new process there is formed a tough, pliable product similar to leather in appearance and in many other properties. The new product will withstand prolonged or hide. I have made the further discovery that a product possessing increased softness and flex:

ibility and an improved appearance is formed where certain special solvents are employed in combination with the active treating agents.

For treatment according to the process of the present invention, I have found that bated or pickled and hairy skins or hides, for example calfskins or steer hides, are very satisfactory.

Skins or hides in other conditions, such as de-,

limed skins or hides, may also be used. For most Tanning by the vegetable method Claims. ('01. 8-94.33)

satisfactory treatment, the hide or skin should have a'pI-I of between about 5 and about 7 prior to treatment. However, skins or hides having a pH somewhat outside these approximate limits may be treated.

Skins or hides of animals generally used for making leather maybe treated according to the process of the present invention. In the speci-.

fication and claims the terms skin or skin material are to be understood in their broad sense as including these materials. The term tanning as employed in the claims is to be understood as covering the process of reacting the treating agents of the present invention with skins or hides to form a leather-like material and is not to be understood as requiring the action of tannic acid or tannins.

Where a pickled material is used, it is first subjected to a conventional depickling operation.

The depickled' skin is then immersed in waterwith agitation to remove dissolved salts and other soluble materials. A suitable treatment period may range from around 2 hours for calfskin to 4 hours for a steer skin.

The depickled and soaked skin is then dried to a moisture content which may be between about 10 and about 15%.

of the skin when subjected to a further drying for 16 hours in air at C. It has been found' that drying is most satisfactorily accomplished by the action of solvents, for example, acetone, methyl acetate, isopropyl alcohol, dioxane, ethylene glycol monomethyl ether acetate or other solvent which will remove the water without seriously harming the skin. This drying may be efiected by leaving the skin immersed in an agitated bath of the solvent overnight. The solvent is then removed from the skin, suitably by evapo ration in a stream of dry warm air.

The above is but one of many conceivable methods for treatment of a skin prior to the treatment with my new agents. Modifications will be readily apparent to persons familiar with the handling of skins. For example, a bated. skin: need not be subject to the depickling and wash-' ing'operations above outlined.

The dried skin is immersed in a body of the liquid treating agent and is maintained in the liquid for a sufficient period to convert the skin to the new leather-like condition.

I have found that the bis-chloroformates of glycols, polyglycols and sulfur-substituted glycols and polyglycols are very effective treating agents. Among compounds in this class are glycol bis-- This moisture content is determined by comparison with the weight.

chloroformate, d1, tri, tetra and dodeca-ethylene glycol bis-chloroformates, tri-methylene glycol bis-chloroformate, and mercapto-ethanol bischloroformate.

Other chloroformates which have been found satisfactory include chloroformates of aliphatic hydrocarbons such as methyl chloroformate, ethyl chloroformate, butyl chloroformate, iso-butyl chloroformate, amyl chloroformate, hexyl chloroformate, lauryl chloroformate and stearyl chloroformate, the aromatic chloroformates such as. phenyl chloroformate and benzyl chloroformate, and c chloro ethyl chloroformate.

I have made the further surprising discovery that skins are converted to a leather-like material having particularly good. resistance to deterioration under the action of water by treating them with chloroformates of higher aliphatic hydrocarbons such as lauryl and stearyl chloroformates having up to 18 carbon atoms.

These treating agents are ordinarily employed as organic solvent solutions in order that. they may penetrate well into the interior of the. skin material, and in order to avoid a too vigorous reaction between the material and. the treating agent. Diethylene glycol monomethyl ether formal has been found articularly satisfactory as a solvent for the treating agent, and solutions comprising it convert skin to particularly soft and fine-appearing, leather-like products. Ethylene glycol monomethyl ether formal and trichlorethylene have been used as solvents with many of applicants treating agents, and the solutions have been found to give very desirable products. Other organic solvents, such as acetone, hexane, carbon tetrachloride, butyl carbitol formal, the diethylene glycol monomethyl ether tetra acetal of glyoxal or toluene, for the agents may be used. A preferred range of concentrations of solutions is from about to. about 50% treating agent by volume based on the volume of the solution.

The time of immersion of the skin in the treating agent varies with the weight and type of skin treated. Preferred times of treatment may vary from about one-half hour to about five hours. In the case of a calfskin, satisfactory action has been obtained by immersion of the prepared, dried, calfskin for about two hours at. 130 F. in a fifty per cent solution of di-glycol bis-chloroformate in diethylene glycol monomethyl ether formal. In the case of steer hide, a four .hour' immersion in the same solution at 130 F. has been found satisfactory.

Comparable effects on these materials have been obtained within the same treating time using as treating agent a fifty per cent solution of di-glycol bis-chloroformate in tri-chlorethylene at room temperature.

As illustrated above, the temperature of the treating bath may vary. Factors controlling the temperature include the boiling points and vapor pressure of the solvents and. of the treating agents and the rate of treating action desired.

After the above treatment, the skin is removed from the treating bath and is immersed in a solvent to remove soluble materials such as ex cess agent, reaction products and the like. Suitable solvents for this use are trichlorethylene,

acetone and toluene.

The skin is removed from thesolvent bath and is permitted to dry. The dried skin is then placed. in a neutralizing bath, which may be a. depickling solution, until it reaches a pHof. about. Tor other value depending uponv the. properties sodium bicarbonate for an hour.

4 desired. This step is desirable in that it also serves to neutralize or decompose acid compounds which may have formed within the skin. The skin is finally washed to remove salts, and is then removed from the washing bath.

The treated skin may be subjected to such further treatments as desired, for example, dyeing, fat liquoring or stuffing, drying and surface finishing.

The following examples are given as illustrative of processes in accordance with the present invention. It is to be understood that the invention is not restricted to the reagents and procedural details disclosed in these examples.

Example 1.--A:steer hide (butt) in the bated condition was immersed overnight in acetone to dry the hide. The hide was removed from the acetone and was subjected to a blast of warm air toevaporate the acetone. The resulting hide had a moisture content of about 10 per cent determined by the method noted above. The dried hide was then immersed in a treating bath at room temperature, the treating bath consisting of 20 parts by volume of di-glycol chloroformate and parts by volume of tri-chlorethylene. After five hours the hide was removed and washed. for two hours in a bath consisting only of tri-chlorethylene. After washing, the hide was removed and allowed to dry and was then. immersed in a bath of 5 per cent sodium bicarbonate in water until the hide reached a pH of about 7. The neutralized hide was removed from the bicarbonate solution and placed in a bath of running water for two hours. The neutralized and washed hide was removed and found to be in a leather-like condition in which it could be subjected to operations following conventional tanning.

Example 2.Pickle.d calfskin was depick-led by immersion in a 5 per cent aqueous solution .of The depickled skin was washed in running water for an hour and dried overnight in a bath of acetone. The calfskin was removed f-rom the acetone and the acetone evaporated from the calfskin by a blast of Warm air. The dried skin was then immersed for two hours in a treating bath at a temperature. of F., the treating bath consisting of 50 parts by volume of tri-ethylene glycol bis-chloroformate and 50 parts by volume of diethylene glycol monomethyl ether formal. The treated calfskin was removed from the bath and washed for two hours in acetone after which it was removed and allowed to dry. The dried calfskin was then immersed in a 5 .per cent solution-of sodium bicarbonate until substantially neutral and was then washed for two hours. in running water. The calfskin was removed from the water and found to. be infa stable non-putresciblecondition in which it could. be subjected to the. usual. operations. which follow tanning.

Example 3.-A calfskin in bated condition was dried overnight in acetone and was removed from. theacetone and subjected to a blast of warm air to evaporate the acetone. The dried calfskin was then immersed in a. bath, consisting of 50 parts by volume of lauryl chloroformate and 5.0 parts by volume of tri-chlorethylene for two hours at room temperature. The treated material was. then washed for two hours in trichlorethylene, removed and allowed to. dry. The driedcalfskin was then neutralized to a pH of about 7 in a5. per cent-solution of sodium bicarbonate.- The. neutralized skin. was finally washed for two hours in running water and gave. a leather-like mate'- rial in condition for the usual operations following tanning. I

Having described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of tanning stock having a moisture content of from to which comprises contacting the stock with an organic solvent solution of an ester of chloroformic acid in an organic solvent, the concentration of the solution being from about 10% to about 50% of the ester of chloroformic acid based upon the volume of the solution.

2. The method of tanning stock which comprises drying the stock by the solvent action of an organic liquid to bring the moisture content down to from about 10 per cent to about 15 per cent and contacting the dried stock with an organic solvent solution of at least one member of the group consisting of bis-chloroformates of glycols and polyglycols, chloroformates of alkyl hydrocarbons having up to 18 carbon atoms, phenyl and benzyl chloroformates, mercaptoethanol bis-chloroformate and [3 chloroethyl chloroformate, the concentration of the solution being from about 10 per cent to about 50 per cent of treating agent based upon the volume of the solution. I

3. The method of tanning stock which comprises drying the stock by the solvent action of an organic liquid to bring the moisture content down to from about 10 per cent to about 15 per cent, contacting the dried stock with a solution of di-glycol bis-chloroformate in diethylene glycol monomethyl ether formal, the concentration of di-glycol bis-chloroformate in the solution being from about 10 per cent to about 50 per cent by volume based upon the volume of the solution, maintaining the stock in contact with the solution for a period corresponding to from about two hours for a calfskin to about four hours for a steer-hide at a temperature of 130 F., removing uncombined di-glycol bis-chloroformate by the action of a solvent, neutralizing acid compounds which may have formed within the stock, Washing the stock to remove neutral salts, and drying the stock.

4. The method of tanning stock which comprises drying the stock by the solvent action of an organic liquid to bring the moisture content down to from about 10 per cent to about 15 per cent, contacting the dried stock with solution of benzyl chloroformate in diethylene glycol monomethyl ether formal, the concentration of benzyl chloroformate in the solution being from about 10 per cent to about 50 per cent by volume based upon the Weight of the solution, maintaining the stock in contact with the solution for a period corresponding to from about two hours for calfskin to about four hours for a steer hide at a temperature of F., removing uncombined benzyl chloroformate by the action of a solvent, neutralizing acid compounds which may have formed within the stock, washing the stock to remove neutral salts, and drying the stock.

5. The method of tanning stock which comprises drying the stock by the solvent action of an organic liquid to bring the moisture content down to from about 10 per cent to about 15 per cent, contacting the dried stock with a solution of lauryl chloroformate in diethylene glycol monomethyl ether formal, the concentration of lauryl chloroformate in the solution being from about 10 per cent to about 50 per cent by volume based upon the weight of the solution, maintaining the stock in contact with the solution for a period corresponding to from about two hours for calfskin'to about four hours for a steer hide at a temperature of 130 F., removing uncombined lauryl chloroformate by the action of a solvent, neutralizing acid compounds which may have formed within the stock, washing the stock to remove neutral salts, and drying the stock.

ROBERT C. PUTNAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 501,235 Seifert July 11, 1893 1,789,322 Roark Jan. 20, 1931 1,826,690 Carroll Oct. 6, 1931 2,080,019 White May 11, 1937 2,127,841 Gellendien Aug. 23, 1938 2,169,513 Brunken Aug. 15, 1939 2,186,889 Ulrich Jan. 9, 1940 FOREIGN PATENTS Number Country Date 461,179 Great Britain 1937 509,703 Great Britain July 19, 1939 447,715 Belgium Oct. 27, 1942 118,155 Australia Jan. 9, 1943 OTHER REFERENCES Richters Organic Chemistry by Spielman, vol. I, pub. 1919 by P. Blakistons Son and Co., Phila., Pa., page 430. 

1. THE METHOD OF TANNING STOCK HAVING A MOISTURE CONTENT OF FROM 10% TO 15% WHICH COMPRISES CONTACTING THE STOCK WITH AN ORGANIC SOLVENT SOLUTION OF AN ESTER OF CHLOROFORMIC ACID IN AN ORGANIC SOLVENT, THE CONCENTRATION OF THE SOLUTION BEING FROM ABOUT 10% TO ABOUT 50% OF THE ESTER OF CHLOROFORMIC ACID BASED UPON THE VOLUME OF THE SOLUTION. 